mS On the Comparative Level of Lakes a^id Seas, 



winter of 182G. After the troublesome and unsatisfiictory experiment 

 of comparing the geodsesical levelling with the barometrical of the year 

 1837, it is impossible to have much confidence in the barometric method 

 employed.* As the Lake Aral has been found to be only 34 feet (5.G 

 toises) above the level of the Black Sea, and that in the two barometric 

 levellings by stations in 1811 and 1837, the error exceeded 224 feet 

 (37.3 toises), it may well be that the Lake Aral may be at the level of 

 the waters of the Caspian, and that all the Aralo- Caspian basin has a 

 depression of 76 feet ( — 12.7 toises). But without adopting this conclu- 

 sion, grounded upon the analogy of the barometrical operations of 1811, 

 1826, and 1837, and excluding also the whole shores of Lake Aral, we 

 still find, as the result of our actual knowledge, an extent of continental 

 land of more than 8000 square marine leagues depressed below the sur- 

 face of the Black Sea. The geodsesical line of zero height, that is to say, 

 that which unites the points of the surface placed on the level of the 

 Black Sea, traverses the Volga between Zaritzin and Saratov. Now, 

 from the extremity of the delta of the Yolga to Zaritzin, there are 3° 40' 

 of latitude — a distance equal to that from Paris to Grenoble, or equal to 

 four- fifths of the extent of Spain. To the east of Zaritzin, the shores of 

 Lake Eltont and Kalmykova, upon the river Jaik, are from 5 to 12 toises 

 below the level of the Black Sea. It is also believed that the country 

 which encloses, to the west of Kalmykova, the salt-lakes of Kamych- 

 , Samara, have a depression of — 23 toises, consequently being ten toises 

 beneath the level of the Caspian Sen.X M. de Struve remarks, ^' that 

 the line of the zero level surrounds a submarine space (placed beneath 

 the surface of the Black Sea) greater even than the surface of the Cas- 

 pian ; and that in the geodsesical levelling of 1836 and 1837, the limits 

 of this vast Asiatic depression towards the west, was at a distance of 12 

 marine leagues from shore. § We have seen that to the north I| and 

 north-east, the depression extends above 70 leagues. Limiting ourselves, 

 then, to an estimate of 8000 square marine leagues less than that of 

 M. de Struve, we obtain for the area of the total depression, — includ- 

 ing that which is actually covered with the waters of the Caspian Sea, 



Duhatnel, was, that the level of the waters of Lake Aral was 117.6 English feet 

 (18.3 toises) above the level of the waters of the Caspian. 



* See an interesting Memoir of M. Lenz : Considerations Mathematiques sur les 

 nivellements par Stations an moyen du barometre. (Bull, de St Petersburg, T. i. 

 p. 51 and 63. 



1 1 have found the south-west extremity of this lake generally very erroneously 

 placed in our maps in lat. 49" 7' 17'^ and long. 44° 15' 36". 



+ Gobel, lieise, T. ii. p. 200. 



§ Bull, de I'Acad. de St Petersb., T. iii. p. 368. 



11 It results from the barometric observations of M. Gobel, considering the zero 

 at the level of the Black Sea, and admitting — 12.7 toises for the Caspian Sea; 

 that the Volga, near to Saratov, is at an elevation of + 6 toises ; Zaritzin is —5 

 toises ; the Steppe Khotchetaevka — 12 t. ; the Lake Bogdo — 3 t. ; the Lake 

 Arsangar + 12 1. ; and the Mount Grand-Bogdo + 87 1. According to MM. Parrot 



